For many years, semiconductor photolithography employed negative tone photopolymers based on the photochemical crosslinking of cyclized poly(isoprene) with bis(arylazide). However, as device geometries became smaller, swelling issues during the solvent development of such resists became increasingly problematic prompting the development of positive tone photopolymers based on diazonaphthoquinone (DNQ)/novolaks. These new photoresists employed an aqueous base solution instead of solvent to develop the image and exhibited essentially no swelling. Thus such photopolymers provided the enhanced image resolution needed to support more advanced semiconductor device fabrication into the mid 1990's (Diazonaphthoquinone-based Resists by R. Dammel, 1993, p. 51).
However, as the industry saw the requirement for geometries that could not be achieved with long wavelength mercury vapor illumination and advanced exposure tools were developed that employed shorter and shorter wavelengths. As these wavelengths approached the deep UV (KrF or 248 nm radiation) the aforementioned DNQ/novolak system was found to be too absorbing and new photopolymers based on poly(hydroxystyrene) (PHS) and chemical amplification strategies were developed leading to transparent, highly sensitive resists (Introduction to Microlithography by L. F. Thompson, C. G. Willson and M. J. Bowden, 1994, p. 212-232 and H. Ito, IBM J. Res. Dev., 2001, 45(5) 683).
Both the DNQ/novolak and PHS systems encompass acidic phenol functionality that is deprotonated by aqueous base, in areas exposed to the actinic radiation, during the image development process thus rendering the resulting ionomer soluble and providing a positive image. Further, it is known that both novolaks and PHS polymers dissolve smoothly in aqueous base developer with minimal swelling (Rao, A. et al. Proc. SPIE, 2006, 6153, 615310-1 and Varanasi, et al. Proc. SPIE, 2005, 5753, 131, respectively).
The use of norbornene-type polymers for forming self-imageable films that are useful for forming structures in microelectronic and optoelectronic devices has also been known (see for example, U.S. Pat. No. 7,022,790). However, such structure forming self-imageable films have generally been limited the use of a solvent based image development process thus limiting both their applicability and use. Given that both the novolak and PHS systems described above successfully incorporate acidic phenol functionality to provide imageability using the industry standard aqueous base development system (0.26N TMAH) for photoresist compositions, it was believed such acidic phenol functionally could be used in a norbornene-type polymer to provide imaging via an aqueous base development system. However, when films of a norbornene polymer containing the essentially identical aqueous base solubilizing functionality of the novolak and PHS systems were immersed in a 0.26 N TMAH solution, the smooth, linear dissolution properties expected were not observed. Rather, the polymer film appeared to be insoluble as peeling of the film was generally observed rather than dissolution thus leaving a residue on the wafer.
As it is believed that aqueous developable norbornene-type film forming polymers and compositions formed thereof will be advantageous for microelectronic and optoelectronic devices, providing such polymers and/or polymer compositions would be useful. Thus solving the aforementioned solubility problems with norbornene-type polymer systems and the creation of polymer compositions and their use is described hereinafter.